Being a professional sportsman is a short career and I don't have a problem with them wanting to get a good pay day, especially towards the end of their careers.
I don't know the numbers involved but lets say, for the sake of argument, they manage to earn an extra £100k in their last 2 years and invest that wisely. Lets also say, again for the sake of argument, that on average they make 2% over and above inflation (that was the long term average, past performance and all that). After 30 years ie when they are in their mid 60s, that would give them about £180k in today's money, not a trifling about. 5% growth comes in at ~£430k.
Of course its trade-offs: uprooting or being separated from families, good clubs help players in to retirement by supporting them look for new careers etc and that itself might be worth more than the extra money in the long term.
We all have/had to make these difficult choices and in my case all those sorts of choices were aimed at giving my family long term financial security if anything happened to me.